Massive black holes interactions during the assembly of heavy sub-structures in the centre of galaxy clusters

We performed a series of direct N-body simulations with the aim to follow the dynamical evolution of a galaxy cluster (GC) ($M_{clus}\simeq 10^{14} M_{\odot}$) in different environment. The results show the formation of heavy sub-structures in the cluster centre in consequence of multiple merging among the innermost galaxies. Moreover we investigate the dynamics of super-massive black holes (SMBHs) residing in the centre of galaxies that form the most massive sub-structure.Comment: 2 pages, 3 figures. To be published in the proceedings of the conference Cosmic-Lab, Modest 201

The origin of the first neutron star -- neutron star merger

The first neutron star-neutron star (NS-NS) merger was discovered on August 17, 2017 through gravitational waves (GW170817) and followed with electromagnetic observations. This merger was detected in an old elliptical galaxy with no recent star formation. We perform a suite of numerical calculations to understand the formation mechanism of this merger. We probe three leading formation mechanisms of double compact objects: classical isolated binary star evolution, dynamical evolution in globular clusters and nuclear cluster formation to test whether they are likely to produce NS-NS mergers in old host galaxies. Our simulations with optimistic assumptions show current NS-NS merger rates at the level of 10^-2 yr^-1 from binary stars, 5 x 10^-5 yr^-1 from globular clusters and 10^-5 yr^-1 from nuclear clusters for all local elliptical galaxies (within 100 Mpc^3). These models are thus in tension with the detection of GW170817 with an observed rate 1.5 yr^-1 (per 100 Mpc^3; LIGO/Virgo estimate). Our results imply that either (i) the detection of GW170817 by LIGO/Virgo at their current sensitivity in an elliptical galaxy is a statistical coincidence; or that (ii) physics in at least one of our three models is incomplete in the context of the evolution of stars that can form NS-NS mergers; or that (iii) another very efficient (unknown) formation channel with a long delay time between star formation and merger is at play.Comment: A&A: accepte

Quenched fractions in the IllustrisTNG simulations: Comparison with observations and other theoretical models

We make an in-depth comparison of the IllustrisTNG cosmological simulations with observed quenched fractions of central and satellite galaxies, for Mstars = 109-12 M⊙ at 0 ≤ z ≤ 3. We show how measurement choices [aperture, quenched definition, and star formation rate (SFR) indicator time-scale], as well as sample selection issues (projection effects, satellite/central misclassification, and host mass distribution sampling), impact this comparison. The quenched definition produces differences of up to 70 (30) percentage points for centrals (satellites) above ∼1010.5 M⊙. At z Z 2, a larger aperture within which SFR is measured suppresses the quenched fractions by up to ∼50 percentage points. Proper consideration of the stellar and host mass distributions is crucial: Naive comparisons to volume-limited samples from simulations lead to misinterpretation of the quenched fractions as a function of redshift by up to 20 percentage points. Including observational uncertainties to theoretical values of Mstars and SFR changes the quenched fraction values and their trend and/or slope with mass. Taking projected rather than three-dimensional distances for satellites decreases the quenched fractions by up to 10 per cent. TNG produces quenched fractions for both centrals and satellites broadly consistent with observations and predicts up to ∼80 (90) per cent of quenched centrals at z = 0 (z = 2), in line with recent observations, and higher than other theoretical models. The quantitative agreement of TNG and Sloan Digital Sky Survey for satellite quenched fractions in groups and clusters depends strongly on the galaxy and host mass range. Our mock comparison highlights the importance of properly accounting for observational effects and biases

Quenched fractions in the IllustrisTNG simulations: The roles of AGN feedback, environment, and pre-processing

We use the IllustrisTNG hydrodynamical simulations to show how the fractions of quenched galaxies vary across different environments and cosmic time, and to quantify the role AGN feedback and pre-processing play in quenching group and cluster satellites. At z = 0, we select galaxies with Mstars = 109-12 M⊙ residing within (≤R200c) massive groups and clusters of total host mass M200c = 1013-15.2 M⊙ in TNG100 and TNG300. The model predicts a quenched fraction of ∼70-90 per cent (on average) for centrals and satellites of mass ≳1010.5 M⊙, regardless of host mass, cosmic time (0 ≤ z ≤ 0.5), cluster-centric distance, and time since infall in the z = 0 host. Low-mass central galaxies (≲ 1010 M⊙), on the other hand, are rarely quenched unless they become members of groups (1013-14 M⊙) or clusters (≥1014 M⊙), where the quenched fraction rises to ∼ 80 per cent. Typically, the fraction of low-mass passive galaxies is higher closer to the host centre and for progressively more massive hosts. The population of low-mass satellites accreted more than ∼ 4-6 Gyr ago in massive hosts is almost entirely passive, thus suggesting an upper limit for the time needed for environmental quenching to occur. In fact, about 30 per cent of group and cluster satellites that are quenched at z = 0 were already quenched before falling into their current host, and the bulk of them quenched as early as 4-10 billion years ago. For low-mass galaxies (Mstars ≲1010-10.5 M⊙), this is due to pre-processing, whereby current satellites may have been members of other hosts, and hence have undergone environmental processes, before falling into their final host, this mechanism being more common and more effective for the purposes of quenching for satellites found today in more massive hosts. On the other hand, massive galaxies quench on their own and because of AGN feedback, regardless of whether they are centrals or satellites

The distinct stellar-to-halo mass relations of satellite and central galaxies: Insights from the IllustrisTNG simulations

We study the stellar-to-halo mass relation (SHMR) for central and satellite galaxies with total dynamical masses above 1010.5 M⊙ using the suite of cosmological magnetohydrodynamical simulations IllustrisTNG. In particular, we quantify environmental effects on satellite populations from TNG50, TNG100, and TNG300 located within the virial radius of group- and clusterlike hosts with total masses of 1012-15.2 M⊙. At fixed stellar mass, the satellite SHMR exhibits a distinct shift towards lower dynamical mass compared to the SHMR of centrals. Conversely, at fixed dynamical mass, satellite galaxies appear to have larger stellar-to-total mass fractions than centrals by up to a factor of a few. The systematic deviation from the central SHMR is larger for satellites in more massive hosts, at smaller cluster-centric distances, with earlier infall times, and that inhabits higher local density environments; moreover, it is in place already at early times (z 2). Systematic environmental effects might contribute to the perceived galaxy-to-galaxy variation in the measured SHMR when galaxies cannot be separated into satellites and centrals. The SHMR of satellites exhibits a larger scatter than centrals (by up to ∼0.8 dex), over the whole range of dynamical mass. The shift of the satellite SHMR results mostly from tidal stripping of their dark matter, which affects satellites in an outside-in fashion: The departure of the satellite SHMR from the centrals' relation diminishes for measurements of dynamical mass in progressively smaller apertures. Finally, we provide a family of fitting functions for the SHMR predicted by IllustrisTNG

Aplicación del índice Z de Palmer para la comparación de sequías en las regiones trigueras II, IV y V Sur de Argentina

p.41-46El Modelo de Palmer se aplica para computar el Indice de Anomalía de Humedad en las tres regiones ecológicas del trigo para analizar las frecuencias de condiciones húmedas, secas y normales. Los valores de los Indices fueron obtenidos para más de 30 localidades con registros de más de 80 años. Para toda la región las condiciones normales oscilan entre el 40 por ciento - 50 por ciento de frecuencias m ientras que las condiciones severas y extrem as alcanzan los mayores porcentajes en la región V Sur. Se presentan mapas m ensuales y estacionales con probabilidades observadas para las mismas categorías de sequías. En general hay valores coherentes entre las regiones especialmente durante la primavera . En algunas localidades se obtienen valores de probabilidades más alto de los esperado

El índice de anomalía de humedad z y su relación con el rendimiento de trigo en Bordenave (Buenos Aires, Argentina)

Se presenta un modelo de regresión lineal para estimar el rendimiento de un cultivo de trigo sembrado en la región subhúmeda seca de la Provincia de Buenos Aires. Se efectuó el ajuste con datos del período 1965-1991 En ese período se introdujeron cultivares con germoplasma mejicano y nuevas tecnologías en el sistema de labranza y sanidad del cultivo.El modelo contiene factores tecnológicos y agroclimáticos. El componente tecnológico del modelo se lo incluyó como un término lineal, estando el término agroclimático constituido por variables independientes que provienen del balance hidrológico propuesto por Palmer . La ecuación de pronostico permite estimar el 82 4% de la variación del rendimiento,con un error standard de estimación de 1,43 qq/ha, resultados que fueron validados con información adicional

Galaxy clusters in presence of dark energy: a kinetic approach

Context. The external regions of galaxy clusters may be under strong influence of the dark energy, which was discovered by observations of supernovae Ia at redshift z < 1. The presence of the dark energy in the gravitational equilibrium equation, with the Einstein Λ term, balances the gravity, and extends the equilibrium configuration more in radius. Aims. We investigate the features of the equilibrium configurations to analyse how the presence of the dark energy affects the density profiles and radial extension by specifying the conditions for which the gravitational equilibrium begins. Methods. We derived the kinetic equation for an equilibrium configuration in presence of dark energy and solved the gravitational equilibrium equation by considering a Maxwell-Boltzmann distribution function with a cut-off in the framework of the Newtonian regime, because the observed velocities of galaxies inside a cluster are much lower than the velocity of light. Results. The prevalence of dark energy effects on the gravity shows a wide region in the W0–ρΛ diagram where equilibrium solutions are not possible. In these particular conditions, the galaxies located in the external regions of a cluster can flow out, following the accelerating expansion of the Universe